Power to a detached garage

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  #1  
Old 07-02-04, 12:16 PM
Skirt283
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Power to a detached garage

Okay, I have been reading a few other posts on this subject and here is my situation. I have a 200 amp entrance in my house with a few open positions left. I have a 100 amp panel that I will be installing in the garage. Total length of wire needed would be 65'. I plan on running this underground in schedule 40 PVC (1 1/2"). I'm only looking to run 60 amps to the garage at the moment. Can I just install a double pole 60 amp breaker in the house and run this to my panel in the garage? I would like the wire size to be big enough for 100 amps (if I should ever need to upgrade. No sense in digging twice).
 
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  #2  
Old 07-02-04, 05:49 PM
Spark Chaser
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The breaker that you add to the house panel needs to be 100 amp - The #2 copper wire that you will be using will not fit under a 60 amp lug - The breaker in the main at the Garage will accomadate #2 Wire - 1 1/4 conduit is too small for that long of a run in my opinion.
 
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Old 07-02-04, 06:02 PM
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I always like to plan ahead, but you should be sure you're willing to pay the price for preparing for 100 amps. Using #2 in large conduit will be a lot more effort and money than just direct burying the 6/3 UF-B you'd need for 60 amps.

Unless you plan a monster welder or several kilns, it is unlikely that you will ever need 100 amps (24KW). Most people can get by quite nicely on 60 amps (14.4KW) in their garage.
 
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Old 07-03-04, 04:44 AM
Spark Chaser
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If you mount a 60 amp breaker in the house panel - then you need to change the main in the garage panel to 60 amp or less.
 
  #5  
Old 07-03-04, 05:10 AM
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Spark Chaser, that is not correct. A main _disconnect_ is required in a detached structure, but _not_ a main _circuit breaker_. An over rated circuit breaker can be used as the main disconnect, if the _required_ overcurrent protection is provided elsewhere.

In the present case, Skirt283 could buy a 100A panel, sold with a 100A main breaker. A 60A feeder is run to this panel, properly protected with a 60A breaker at the main panel. The 60A breaker would provide overcurrent protection for the feeder and the sub-panel. The 100A breaker would be used only as a disconnect switch.

In general it is desired to 'coordinate' breakers, both by amp rating and by time-trip curve rating, so that the breaker which trips is the one closest to the fault, and the fewest number of loads is effected. Ideally if you overload a circuit in your kitchen, then breaker to that circuit will blow, rather than your main house breaker...this is an example of coordination. However in this case, coordinating breakers would be more expensive, and would waste feeder capacity, and would not provide any benefit in terms of restricting the fault to a smaller set of circuits.

-Jon
 
  #6  
Old 07-03-04, 07:44 AM
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Originally Posted by Spark Chaser
The breaker that you add to the house panel needs to be 100 amp - The #2 copper wire that you will be using will not fit under a 60 amp lug - The breaker in the main at the Garage will accomadate #2 Wire - 1 1/4 conduit is too small for that long of a run in my opinion.
According to my copy of the Square D catalog (I don't really know what brand of main panel Skirt283 has, but if it is Squared D, this probably applies), both QO and HOM breakers in the range of 35 to 70 amps will take a single conductor sized from #8 to #2. 80 to 125 amps will take #4 to #2/0.

My copy of the Cutler-Hammer catalog shows that CH breakers will take #14 to #2 in 40 to 70 amps, and #10 to #1/0 in 80 to 125 amps. The BR series will only take #2 at 60 amps and up (to #1/0 up to 110 amps, and to #2/0 in 125 and 150 amps).
 
  #7  
Old 07-03-04, 04:02 PM
Spark Chaser
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Winnie - I must have read it different than you did - He wanted to Run wire big enough for 100 amp for future upgrades - My practice has always been - Example - In a 3 phase Buss Head - 100 amp fuses - Then put 90 amp fuses in the Disconnect on the floor so that if you had a fault - The fuses on the floor would normally blow 1st. - I guess in his case - If he had a fault in the garage that was serious enough to take out the main - It would kick the one in the house first if it were a 60 amp breaker - maybe I really don't have anything to offer here - Maybe I just need to back off - Sorry if I offended anyone.
 
  #8  
Old 07-03-04, 05:15 PM
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I always suggest that we clearly differentiate between a requirement and a recommendation. Statement such as a breaker "needs to be 100 amp" or that "you need to change the main" might be misinterpreted by some people as requirements, when they are in fact only recommendations.

Any time somebody makes a recommendation sound like a requirement, a clarification is warranted.
 
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Old 07-05-04, 07:57 AM
Skirt283
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Thumbs up Thanks

I'll be upgrading the wire size to #2 and increasing the size of the conduit to accommodate this larger size. As stated in one of the posts the breaker from the main panel in the house will also need to be upgraded to a 100 amp. Digging is not a problem for me, I have a Bobcat with a trencher attachment. I know that I will probably never need 100 amps at the garage (24' x 28' with an additional 18' x 28' room on top). But I have seen too many times where as someone doesn't plan for things in the future and end up causing them selves more work. Just like most of the older homes built around here only having 100 amp entrances. Not too many people 50 years ago ever thought they would have central air, a microwave, several TV's, computers and the like. To everyone who replied... Thank you for your time and I appreciate all of the advice.
 
  #10  
Old 07-05-04, 08:18 AM
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Nothing wrong with 'oversizing'. Since you have decided to spend the money laying conduit, I would strongly suggest that you run _two_ conduit, one for your power wiring, and one for anything else you care to pull, eg network or phone wiring.

In addition, you should never put together conduit and conductors at the same time, but instead you should assemble the complete conduit system, and then pull the conductors into the conduit. You should have no more than 360 degrees of bend between pull points, ideally much less (the fewer the bends and the shallower the bends, the easier the pulling job.) The solvent glue used to put together PVC conduit can damage the insulation on the wires.

Always pull a complete set of conductors through the conduit, rather than one conductor at a time.

Since you are pulling the conductors through the conduit, you can install conduit large enough for a 100A feeder, but then pull conductors sufficient for 60A. In the future, should you need to expand, you won't need to dig again, but you will need to pull larger conductors. This is a halfway point that allows for easier future expansion, but don't spend the full price for the future expansion.

-Jon
 
  #11  
Old 07-06-04, 05:01 AM
rlrct
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The difference in cost between running #6 and #2, plus upsizing the breaker in the main panel from 60 to 100 amps is under $60 at our local HD.

If you're going to the work of digging a trench, running conduit, pulling wire - isn't it worth $60 to just put in a full 100 amp subpanel now and be done with it?

Your time's valuable and, if nothing else, I'd certainly pull the larger conductors. You're spending the money for the larger conduit and fittings anyway.

YMMV.
 
  #12  
Old 07-19-04, 05:42 AM
Skirt283
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Thumbs up Finished

Finished the project this weekend. Ran #2 wire through 2" conduit. Also ran my cable and phone line in the same trench but in a separate conduit. Now all I need to do is to find the time to wire the garage. I have a friend who is an electrical contractor... and he owes me a few favors. Thank you to all who replied. I appreciated the help.
 
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